Modern computer systems support communications at many different levels. An individual computer comprises a variety of different processors communicating with each other. A single central processing unit (CPU) is typically the basic workhorse of the computer, but other processors control disk storage devices, printers, terminals, communications with other computers, etc. Even more remote and primitive processors may control other functions, such as monitoring sensors, input keypads, etc. In addition, multiple computer systems may be connected to a network, whereby they may communicate with each other. Each of these processors or systems must have some defined path for communications.
The design requirements for communications paths vary. For example, where a communications path must pass a large volume of data over a relatively short distance, such as the path from a disk storage controller to main memory, a wide parallel bus is usually employed. On the other hand, a low volume path to a more remote device calls for a less expensive method, usually a serial communications protocol.
In certain applications there is a need for a low volume communications network enabling a plurality of nodes to send occasional messages to each other. A typical such application is a network of monitoring nodes connected to a master control node, in which each monitoring node contains a microprocessor which monitors the status of, and makes occasional adjustments to, some set of physical parameters. In such a network, the central control node must be made aware of any status changes and must be able to issue adjustment commands to the monitoring nodes. While it is not necessary that such a network be able to support a high volume of network traffic, it must be able to communicate quickly and reliably when there is a status change.
In the type of network application described above, it is desirable to hold the cost of the network as low as possible while providing the required capabilities. A variety of serial communications protocols exist. However, these protocols either require more hardware than minimally necessary, or do not provide the desired degree of function or reliability.
It is therefore an object of the present invention to provide an enhanced method and apparatus for communicating among a plurality of nodes in a network.
Another object of this invention is to reduce the cost of communicating among a plurality of nodes in a network.
Another object of this invention is to increase the reliability of a low cost, low volume communications network.
Another object of this invention to provide an enhanced method and apparatus for communicating among a control node and a plurality of monitoring nodes in a monitoring network.
Another object of this invention is to reduce the cost of communicating among a control node and a plurality of monitoring nodes in a monitoring network.
Another object of this invention is to increase the reliability of a monitoring network comprising a control node and a plurality of monitoring nodes.